Electromagnetic load compensated weighing apparatus including damping

ABSTRACT

Weighing apparatus of the electromagnetic load compensation type including a vertically movable load suspension member, characterized by the provision of damping means for damping pendulum oscillations of the load suspension member when said member is in a given damping position relative to the frame of the apparatus, and control means for interrupting the weighing operation of the apparatus and for utilizing the electromagnetic load compensating means to place the load suspension member in the damping position.

United States Patent Baumgartner 51 July 18, 1972 ELECTROMAGNETIC LOAD2,940,747 6/1960 Eder et al. ..177/2l2 CONIPENSATED WEIGHING 3,133,6065/1964 Thomson ..177/212 RA u 3,172,493 3/1965 Von Koch et a1... 177/185APP TUS INCLUDING D ING 3,355,015 11/1967 Cervin ..l77/l84 [72]lnventor: Max Baumgartner, Etzelstrasse 4, CH- 3,519,095 7/1970 Tomes..l77/212 8712, Stafa, Switzerland Primary Examiner-Robert S. Ward, Jr.[22] led: May 1971 Attorney-Lawrence E. Laubscher [21] Appl. No.:145,718 [57] ABSTRACT I [30] Foreign Application Priority Data Weighingapparatus of the electromagnetic load compensation type including avertically movable load suspension June 18, Switzerland membercharacterized the provision of damping means for damping pendulumoscillations of the load suspension [52] 0.5. CI ..l77/l88, 177/210,177/212 member when said member is in a given damping position 51] In Cg U 3 /0 g 23/0 relative to the frame of the apparatus, and controlmeans for [58] Field of Search ..l77/ 184, 185, 187-189, interruptingthe weighing operation of the apparatus and for 177/210, 212 utilizingthe electromagnetic load compensating means to place the load suspensionmember in the damping position. [56] References Cited l0 Chins, 2Drawing Figures UNITED STATES PATENTS 2,661,201 12/1953 Bowes ..l77/l883 4 L VA 13 12 Q P r :2 a: l 1 N5 m 16 15 8 7 14 lg 11 -11 M PatentedJul 18, 1972 2 Sheets-Sheet l lhv'em o m5 MAI 14 flH-orneq Patented July18, 1972 3,677,357

2 Sheets-Sheet 2.

Max Bumgm+ner ELECTROMAGENTIC LOAD COMPENSATED WEIGHING APPARATUSINCLUDING DAMPING This invention relates generally to electromagneticweighing apparatus, and more particularly, to weighing apparatus whichoperates on the principle of electromagnetic load compensation.

Weighing apparatus of this kind are generally in the form of beambalance weighing machines. Conventional constructions include at one endof the balance beam load means comprising suspension means and/or aweighing pan, and at the other end there are provided electromagneticmeans for load compensation (for example, in the form of a moving coilsystem), indicating means being provided for indicating the position ofthe balance beam (for example in the form of an inductive sensingsystem).

In order to achieve the degree of precision which is required,particularly in the case-of micro and ultra-micro weighing machines, itis necessary inter alia to damp troublesome oscillations. Theoscillations of the balance beam in the direction of inclination andthus the longitudinal oscillations of the load portion are damped by thecompensation system itself, so that special devices for'that purpose arenot required. The same also applies to beam-less weighing machines, asregards the longitudinal oscillations of the load portion.

However, the situation is different in the case of pendulum oscillationsof the weighing pan and the suspension means, which oscillations can beproduced, for example, by external vibration. The damping efi'ect whichcan be achieved for example, by using taut straps of suitable rigidityfor suspending the load portion is not sufficient to meet therequirement for rapid oscillation damping. This requirement is of greatimportance, with a view to achieving the highest possible weighingspeeds in individual weighing operations and the shortest possibleinterruptions in reproducing meaningful measuring results when carryingout long-duration gravimetric experiments.

This gives rise to the necessity of an additional damping device for theload portion.

Damping devices of that kind are known per se in the case ofconventional beam weighing machines, whether in the form of weighing panbrake means which act upwardly on the weighing pan (as disclosed, forexample, in the German Pats. Nos. 965,081 and 1,045,675, and the BritishPat. No. 771,0l), or suspension braking means (for example German Pat.No. 1,246,264 and U.S. Pat. No. 3,074,498). These damping devices areall brought into operative connection by mechanical means. Concerningelectromagnetic weighing machines, however, it proves to be useful notto operate the said damping devices mechanically. Mechanical operationwould cause in this case a rather expensive construction. Moreover, incertain cases, e.g., for weighing in a vacuum, there would ariseadditional difiiculties in design.

Accordingly, a primary object of the present invention is to provideimproved weighing apparatus which operates on the principle ofelectromagnetic load compensation, comprising a load portion formed bysuspension means and/or a weighing pan, mechanical damping means fordamping pendulum oscillations of the load portion, electromagnetic loadcompermation means, and means for controlling the load compensationmeans to interrupt the weighing operation and bring about operation ofthe damping means.

Preferably the damping means comprises a movable portion fixed to theload portion of the machine, and a fixed portion, and the damping meansis brought into operation when the I load portion is moved vertically tobring the two portions of charges, which may be found necessaryparticularly when carrying out long-duration gravimetric experiments inparticular media or in a vacuum, as certain fonns of micro andultramicro weighing machines have non-conductively arranged suspensionmeans. Thus, in many beam weighing machines, the suspension means arecarried on the balance beam by way of sapphire bearings.

It is also possible for initiation of the variation in compensationforce, which variation produces the damping connection, to be renderedautomatic for some cases, for example when the course of a long-durationweighing operation is plotted by way of a recording pen and theregistration curve is rendered discontinuous due to sudden vibration andconsequent oscillations of the load portion. By taking suitableprecautions, the

above mentioned variation in compensation force can be' producedautomatically in such cases.

In a further aspect of the invention, it is found desirable for theoperation as such of varying the compensation force to be varied,depending on specific requirements. 1n the simplest case the variationconsists of a sudden reduction in the compensation current, whereuponthe load portion of the weighing machine will move downwardly with ajerk under the effect of its weight until reaching the damping positiondefined for example by a mechanical stop. Likewise, the load portionwill move relatively rapidly upwardly after the original value of thecompensation current has been restored. In cases in which a rapidmovement of this kind is not desired, means can be provided to allow theload portion to return gradually into the weighing position, andpossibly also similarly as regards deflection of the load portion intothe damping position. In this way, any secondary oscillations whichmight be produced as a result of the jerky movements of the load portionare avoided.

It may further de desirable for the variation in the compensationcurrent to be adapted by suitable means to the particular weighingrange, in order to obtain movements which are always substantiallyidentical.

Other objects and advantages of the invention will become apparent fromthe following specification when viewed in the light of the accompanyingdrawing, in which:

FIG. 1 is an electrical schematic diagram of a first embodiment of theinvention; and

FIG. 2 is a similar schematic diagram of an alternate embodiment of theinvention.

Referring first to FIG. 1, the balance beam 3 is pivotally mounted atthe fulcrum point 4 and carries at one end the suspension means 5 thatsupport the weighing pan 6 which receives the material 7 to be weighed.Secured to the suspension means 5 is a movable damping element 8 which,upon lowering of the suspension means 5, comes into operative dampingengagement with the friction faces 9 of the stationary damping element10 which is mounted on the fixed part 11 of the weighing machine. I

Arranged at the other end of the balance beam 3 is the compensationmeans including a ferromagnetic armature 12 carried by the fixed part 11of the weighing machine, and the moving coil 13 connected with the freeend of the beam 3.

A lug 14 secured to the beam 3 extends between the stationary pair ofcoils l5 and 16. Coil 15 is supplied with highfrequency alternatingcurrent from the oscillator 17 and induces in the coil 16 analternating-current voltage which is dependent on the position of thelug 14 and which is fed to the amplifier l8, rectified by the rectifierl9 and applied to the differential amplifier 20 via the bridge circuitincluding resistors 21, 21', 22, 22'. In the illustrated weighingposition of the switch 23, the voltage difference'at the amplifier 20 isdetermined by the position of the lug 14 (actual voltage) and bythevalue of weighing resistor 21' (reference voltage) relative to resistor21. The amplifier 20 supplies the necessary current for the compensationcoil 13 until the voltage difference, apart from the regulating error,becomes zero (that is to say, when a condition of equilibrium isachieved). The coil current is a measure of the weight of the material 7and is indicated in units of weight by way of digital voltmeter 24 orsimilar indicator means.

When the switch 23 is operated, the voltage difierence, independently ofthe weight of the load portion, is determined in accordance with asecond reference voltage that is a function of the value of dampingresistor 22 relative to resistor 22. This second reference voltage is soselected that the actual voltage which corresponds thereto and which isdetermined by the position of the lug 14 will be achieved when the twodamping elements 8 and 9 come into operative connection, by virtue ofthe inclination of the balance beam 3.

OPERATION Assume that the first reference voltage established byresistor 21' is such that when the pan 6 is empty and the balance beam 3is in a balanced equilibrium position, the output voltage of amplifier20 equals zero. Assume also that the second reference voltageestablished by resistor 22' is such as to produce a current flow in coil13 which will result in beam 3 being pivoted to lower suspension meansto the damping position in which movable damping element 8 engagesstationary damping elements 9.

As material 7 is added to the pan 6 with switch 23 in the illustratedweighing position, beam 3 pivots in the counterclockwise direction todisplace lug 14 upwardly relative to the coils 15 and 16, whereby theinput voltages to amplifier are unbalanced, and amplifier 20 presents anoutput voltage to coil 13 that tends to return beam 3 to the equilibriumposition. The amplitude of this coil current, as indicated by the meter24, is a function of the weight of the material deposited in the pan.

To damp pendulum oscillations of the pan 6 and suspension means, switch23 is operated (manually or mechanically) to the damping position,whereupon a second output current is provided by differential amplifier20 that is a function of the second reference voltage produced byresistor 22'. The flow of this output current through coil 13 causesbeam 3 to be pivoted to lower suspension means 5 to the dampingposition, whereupon movable damping element 8 engages stationary dampingelement 9. When switch 23 is returned to the weighing position, thefirst reference voltage is again supplied to the amplifier 20 forcomparison with the voltage signal from coil 16, and the weighingoperation is resumed.

Referring now to FIG. 2, the second embodiment is characterized by thearrangement of the first pair of resistors 21, 21 between the amplifiersl8 and 20, and the second pair of resistors 22, 22' between theamplifier 20 and the indicator means 24. Consequently, the compensationcurrent of the moving coil 13 is directly reduced to produce theoperative connection of the damping means 8, 9.

The figure again shows switch 23a in the position which corresponds tothe weighing operation. In order to damp oscillations of the suspensionmeans, the switch 23a is operated and the coil current is now determinedby the size of the resistor 22' relative to that of resistor 22.

In both arrangements, the weight indicator means 24 does not supply anymeaningful result during the oscillation damping action (i.e, during theestablishment of the second reference voltage determined by the resistor22 Further uses of the principle according to the invention are obvious(as, for example, in beamless electromagnetically compensating weighingapparatus).

While in accordance with the provisions of the Patent Statutes thepreferred forms and embodiments of the invention have been illustratedand described, it will be apparent that various changes may be madewithout deviating from the inventive concept.

What is claimed is:

l. Weighing apparatus, comprising a frame (1 l support means including avertical load suspension member (5) connected with said frame formovement in a weighing direction upon the application of a weighingforce thereto;

electromagnetic load compensating means (12, 13) for applying to saidsupport means a compensating force in opposition to said weighing force;

mechanical damping means (10) operable when said load suspension memberis a given damping position relative to said frame for damping pendulumoscillations of said suspension member; and

control means for temporarily interrupting the weighing operation ofsaid apparatus and for operating said electromagnetic load compensationmeans to place said load suspension member in said damping position.

2. Apparatus as defined in claim 1, wherein said load compensation meansincludes means (21') establishing a reference voltage to effect anequilibrium condition of said support means relative to said frame, saidcontrol means being operable to vary said reference voltage to causeoperation of said mechanical damping means.

3. Apparatus as defined in claim 2, wherein said load compensation meansincludes armature (l2) and compensating coil (13) elements one of whichis connected with said frame and the other of which is connected withsaid support means, respectively, said damping operation being affectedby variation of the current in the said compensating coil.

4. Apparatus as defined in claim 1, wherein said electromagnetic loadcompensating means comprises associated armature (l2) and compensatingcoil (13) portions one of which is connected with said frame and theother of which is connected with said support means, respectively, andmeans for effecting a flow of current through said compensating coil asa function of the degree of displacement of said support means by saidweighing force from an equilibrium position relative to said frame.

5. Apparatus as defined in claim 4, wherein said means for effectingflow of current through said compensating coil comprises associatedsensing coil and metal lug elements (l4, l5, 16) at least one of whichis connected with said frame and the other of which is connected withsaid support means.

6. Apparatus as defined in claim 5, and further including equilibriumbalancing means for causing the current flow through said compensatingcoil when said support means is in the equilibrium position relative tosaid frame, said equilibrium balancing means including means (21)establishing a first reference voltage, and means (20) for comparing thesignal from said sensing coil with said first reference voltage toproduce a resultant control voltage that is applied across saidcompensating coil.

7. Apparatus as defined in claim 6, wherein said control means furtherincludes means (22') establishing a second reference voltage, and switchmeans (23) for substituting said second reference voltage for said firstreference voltage, thereby effecting displacement of the load suspensionmeans to the damping position.

8. Apparatus as defined in claim 6, wherein said control means furtherincludes means (22) establishing a second reference voltage, and switchmeans (23a) for isolating said comparison means from, and for connectingsaid second reference voltage to, said compensating coil.

9. Apparatus as defined in claim 1, wherein said support means includesa balance beam (3) pivotally connected intermediate its ends with saidframe, said suspension means being suspended frome one end of said beamand said electromagnetic load compensation means being arranged adjacentthe other end of said beam.

10. Apparatus as defined in claim 4, and further including indicatingmeans responsive to the flow of current through said load compensatingmeans for indicating the weight of an object positioned on said loadsuspension member.

iiNITED STATES, PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.-,677, 7 Dated Jul 18 1972 In ent flx) Max Baumqartner It is certifiedthatetror appears in the above-identified patent and that said- LettersPatent are hereby correc ted as shown below:

the Heading:

, Assignee': Mettler Instrumente AG, Zurich, Switzerland Signed andsealed this 17th day of April 1973.

(SEAL) Attest:

EDWARD M.FLETCHERT,JR. 7 ROBERT GOTTSCHALK Attesting OfficerCommissioner of Patents FORM PC4050 USCOMM-DC wan-P69 fl' U45.GOVERNMENT PRINTING OFFICE I I9! 0-355-331,

UNITED STATES PATENT OFFICE- CERTIFICATE OF CORRECTION Patent No. 3 357Dated July 18, 1972 Inv t flx) Max Baumqartner It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

i In the Heading:

Assignee: Mettler Instrumente AG, Zurich, Switzerland Signed and sealedthis 17th day of April 1973.

(SEAL) Attest:

EDWARD M. FLETCHERQJR. R ROBERT GOTTSCHALK Attestlng OfficerCommissioner of Patents USCOMM-DC BD376-P69 w U.S. GOVERNMENT PRINTINGOFFICE I969 0-366-335,

F ORM PC4050 (10-69)

1. Weighing apparatus, comprising a frame (11); support means includinga vertical load suspension member (5) connected with said frame formovement in a weighing direction upon the application of a weighingforce thereto; electromagnetic load compensating means (12, 13) forapplying to said support means a compensating force in opposition tosaid weighing force; mechanical damping means (10) operable when saidload suspension member is a given damping position relative to saidframe for damping pendulum oscillations of said suspension member; andcontrol means for temporarily interrupting the weighing operation ofsaid apparatus and for operating said electromagnetic load compensationmeans to place said load suspension member in said damping position. 2.Apparatus as defined in claim 1, wherein said load compensation meansincludes means (21'') establishing a reference voltage to effect anequilibrium condition of said support means relative to said frame, saidcontrol means being operable to vary said reference voltage to causeoperation of said mechanical damping means.
 3. Apparatus as defined inclaim 2, wherein said load compensation means includes armature (12) andcompensating coil (13) elements one of which is connected with saidframe and the other of which is connected with said support means,respectively, said damping operation being effected by variation of thecurrent in the said compensating coil.
 4. Apparatus as defined in claim1, wherein said electromagnetic load compensating means comprisesassociated armature (12) and compensating coil (13) portions one ofwhich is connected with said frame and the other of which is connectedwith said support means, respectively, and means for effecting a flow ofcurrent through said compensating coil as a function of the degree ofdisplacement of said support means by said weighing force from anequilibrium position relative to said frame.
 5. Apparatus as defined inclaim 4, wherein said means for effecting flow of current through saidcompensating coil comprises associated sensing coil and metal lugelements (14, 15, 16) at least one of which is connected with said frameand the other of which is connected with said support means. 6.Apparatus as defined in claim 5, and further including equilibriumbalancing means for causing the current flow through said compensatingcoil when said support means is in the equilibrium position relative tosaid frame, said equilibrium balancing means including means (21'')establishing a first reference voltage, and means (20) for comparing thesignal from said sensing coil with said first reference voltage toproduce a resultant control voltage that is applied across saidcompensating coil.
 7. Apparatus as defined in claim 6, wherein saidcontrol means further includes means (22'') establishing a secondreferencE voltage, and switch means (23) for substituting said secondreference voltage for said first reference voltage, thereby effectingdisplacement of the load suspension means to the damping position. 8.Apparatus as defined in claim 6, wherein said control means furtherincludes means (22'' ) establishing a second reference voltage, andswitch means (23a) for isolating said comparison means from, and forconnecting said second reference voltage to, said compensating coil. 9.Apparatus as defined in claim 1, wherein said support means includes abalance beam (3) pivotally connected intermediate its ends with saidframe, said suspension means being suspended frome one end of said beamand said electromagnetic load compensation means being arranged adjacentthe other end of said beam.
 10. Apparatus as defined in claim 4, andfurther including indicating means responsive to the flow of currentthrough said load compensating means for indicating the weight of anobject positioned on said load suspension member.